1. Field of the Invention
The present invention relates to a gas insulated switchgear for use in a substation, etc.
2. Description of the Prior Art
FIG. 5 illustrates a conventional gas insulated switchgear which is described on page 379 of "Mitsubishi Denki Technical Report," Vol. 51, No. 6. In this conventional switchgear, main bus bars 1A, 1B and 1C are of A, B and C phases, respectively, (also in the following description A, B and C represent phases) and are disposed horizontally, while branch bus bars 2A, 2B and 2C are connected to the main bus bars 1A, 1B and 1C, respectively, each at the portion m and are disposed on a plane located higher than the main bus bars. To the end portions of these branch bus bars are connected disconnecting switches 3A, 3B, 3C, current transformers 4A, 4B, 4C, and circuit breakers 5A, 5B, 5C. To the portion illustrated on the lower, left end side of the figure are further connected current transformers 4A, 4B, 4C, disconnecting switches 3A, 3B, 3C, bushings 6A, 6B, 6C, and lightning arresters 7A, 7B, 7C. The bushings 6A, 6B, 6C are connected to transmission lines 8A, 8B, 8C. A unit comprising the disconnecting switches 3A, 3B, 3C, current transformers 4A, 4B, 4C, circuit breakers 5A, 5B, 5C, bushings 6A, 6B, 6C, and lightning arresters 7A, 7B, 7C, is called a transmission line unit, which is represented by L.
On the other hand, in the portion illustrated on the upper left side of the figure, further connected to the circuit breakers 5A, 5B, 5C are current transformers 4A, 4B, 4C, lightning arresters 7A, 7B, 7C, and cable head portions 9A, 9B, 9C, to which are connected cables 10A, 10B and 10C. Since a transformer is provided at the front ends of those cables, this unit is called a transformer unit, indicated at T. The unit illustrated in the central lower portion of FIG. 5 comprises disconnecting switches 3A, 3B, 3C, current transformers 4A, 4B, 4C, and circuit breakers 5A, 5B, 5C, and functions to electrically divide the main bus bars, so is called a bus bar section unit, indicated at S.
In this construction, electric power is fed from a generator provided at the front end of the transformer connected to the transformer unit T and is supplied to the constituent units through the main bus bars 1A, 1B and 1C, then is transmitted to transmission lines from the transmission line unit L. In some case, the above construction is used as a power receiving equipment wherein electric power is received from the transmission line unit L and then fed to each transformer unit T through the main bus bars 1A, 1B and 1C. As the case may be, the circuit breakers and disconnecting switches of the bus bar section unit S are opened and the main bus bars 1A, 1B and 1C are operated as independent circuits. Further, in the event of a fault, the circuit breakers are opened to isolate the fault point, while the operation of a sound portion is continued.
Since the conventional gas insulated switchgear is constructed as above, a relatively wide ground area is required and it is necessary to use long main and branch bus bars, thus leading to the increase of cost. Besides, the probability of failure becomes larger because of a very long electrical insulating portion. Further, there is the problem of deteriorated dielectric strength caused by the inclusion of metallic particles into gas. The bus bars arranged horizontally are apt to be influenced thereby.